1. Field of the Invention
The invention relates to printing presses, and more particularly to a wear-resisting, ink-repellent coating process for printing-press components.
2. Description of the Related Art
In various areas of a printing press, there is a need for surfaces which have a high resistance to wear resulting from sliding movements of the paper and, at the same time, these surfaces must not become wet either by absorbed or fresh offset printing ink.
The deposition of ink ultimately results in a change in the dimensions of the components to which it is applied. As a result, in addition to smearing of the printed paper, precision also declines until ultimately the folding unit, for example, fails to function. Increasing paper speeds intensifies both the wear problem and the problem of ink deposition.
The same can also be said of the sheet turner, since in this component sheets of paper which have been printed on both sides have to be transported in an accurate position and at increasing speeds without any ink being absorbed. With regard to this problem, it has already been attempted, in accordance with DE 29 14 255 A1, to counteract wear and ink deposition by means of special cylinder coatings, consisting of wear-resistant metals or metal oxides, as well as a sealing material which is anchored therein.
In DE 29 14 255 A1, sealing materials mentioned are Teflon and copying ink. However, both sealing materials are known to have an insufficiently long service life in rapid web-fed printing presses and, in the case of Teflon, also lead to substantial heating of the component which is to be coated, which may result in dimensional distortion. The sintering temperature of Teflon is in the region of 300xc2x0 C. and is therefore sufficiently high to cause dimensional distortion on precision rollers, in particular where welded structures are involved.
Ink-repellent surface properties are required not only to convey the printed paper in the printing press, but also, in the case of waterless offset printing (also known as the TORAY process), for substituting the film of dampening solution on the printing plate in the form of a silicone film. The term silicone encompasses a substantial group of synthetic polymeric compounds in which silicon atoms are crosslinked in chain and/or network form via oxygen atoms, and the remaining valences of the silicon being saturated by hydrocarbon radicals (usually methyl groups). Another name for silicones is polyorganosiloxanes.
In addition to their virtually perfect ink-repellent properties, these silicone films on the waterless printing plates also have a surprisingly high resistance to abrasion. This is a result of the fact that in numerous modern presses the so called delta effect is used to eliminate printing residues, such as for example grains of paper or dust. The delta effect is nothing other than a slight slippage, in the percentage range, between the roller for applying dampening solution and the plate cylinder and is described extensively in U.S. Pat. No. 4,724,764.
The invention is based on the object of finding a seal for low wear coatings on printing press components which provides a permanent ink-repellent surface quality and, in addition, has a high resistance to standard cleaning agents used in printing technology.
This and other objects are achieved in accordance with the present invention wherein the wear-resisting ink-repellent coating for printing press components comprises a wear resistant material in the form of one of metal oxides and low-wear hard metals, and a sealing material for treating the wear resistant material. The sealing material comprises a polyorganosiloxane sealant that cures in a temperature range of 100xc2x0 C. to 170xc2x0 C.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.